A MEMS (Micro-Electro-Mechanical-System) device is a micro-sized electro-mechanical structure having fabricated by various microfabrication processes mostly derived from integrated circuit fabrication methods. Such a system may also include electronic circuits fabricated together with such a structure to perform a complete function, usually that of a sensor or an actuator. The developments in the field of microelectromechanical systems (MEMS) allow for the bulk production of microelectromechanical scanning mirrors and scanning mirror arrays that can be used in all-optical cross connect switches, 1×N, N×N optical switches, variable optical attenuators, laser displays, bio-medical imaging, etc. A number of microelectromechanical mirror arrays have already been built using MEMS production processes and techniques. These arrays have designs that fall into approximately three design categories. A desirable component of many MEMS devices is an actuator that provides for either tip-tilt (2 degrees of freedom) or tip-tilt-piston (3 degrees of freedom) actuation.
Utilizing gimbaled structures is the most common method of implementing two-axis (two degrees of freedom, 2DoF) rotation, although packaging-based methods are utilized as well. However, to implement 2DoF gimbaled micromirrors without cross talk between driving voltages, electrical isolation and mechanical coupling is necessary. Backfilling of isolation trenches by depositing an additional dielectric layer and chemical mechanical polishing (CMP) has been used to achieve the electrically isolated mechanical coupling. However, the additional deposition and CMP steps significantly increase complexity and cost. Another viable method is to leave part of the handle wafer unetched beneath the gimbal structure. In all cases, complex fabrication has been required, and relatively low frequencies have been achieved due to the gimbals' slow outer axis. In applications where high speed static scanning is required the previous methods do not provide adequate solutions.
In single-axis and two-axis devices it is always important to increase torque (force) for rotation such that larger angles of rotation can be achieved or higher speeds can be attained by the device. If the individual rotating actuators can have more torque it will allow the designer to use stiffer support and torsion beams which will in turn increase the device bandwidth and resonant frequencies. Therefore we invented methods for combining forces of multiple actuators as well as methods for providing bi-directional torque within a single actuator. Further, we invented methods to further stabilize devices for desired axes of rotation, especially in the case of one-axis tilt devices.
Another focus of the designer of scanning mirror devices is flatness and stability of the reflecting mirror itself. Since this mirror may be fabricated separately from the actuator and then assembled (bonded) to the actuator, it is important to design each of them in such a way that upon final assembly the final unit has good mirror properties such as static flatness and minimal dynamic deformation.
It is within this context that embodiments of the present invention arise.